Battle of Britain remake of PSS game CodeSVN

Landing menu now warns when airfield is closed or its runway damaged. Squadron can't choose to land on closed airfield.

Refueling and rearming time now affected by amount of damage inflicted to airfield.

Added hidden German airfields at the eastern edge of the map - these will be their starting positions in regular game. German squadrons can land now and be refueled and rearmed.

Bombing airfields: added destroying planes on ground by attacking Luftwaffe bombers.
Added mission target X and Y coordinates to starting data of squadrons (data which is read from file).

Trying some code to destroy planes present on airfield that is being bombed.

Minor bug fix and adjustments to bombing sequence.

Planes bombs their targets. Checks if individual bomber hit its target and how much damage is inflicted. Changes statuses of targets based on damage inflicted.
Still needs some testing. Minor bugs present.

Airfield.java: first draft of inflictDamage method

Removed unused variable.

Bombing sequence: adding experience for bombing, expending ammo (bombs).
Created new variable in Squadron.java: pilotsExperienceBombing - experience in performing bombing mission as opposed to experience in air combat (pilotsExperience).